1. Field of the Invention
The present invention relates to a method of forming color photographic images, and more particularly to a method of forming color photographic images using a novel yellow color forming coupler.
2. Description of the Prior Art
It is well known that color forming couplers couple with oxidation products of primary aromatic amino developing agents to form color photographic images. Most conventional yellow color forming couplers are four-equivalent couplers and these couplers require four moles of exposed silver halide as an oxidizing agent to form one mole of azomethine dye. An introduction of a large amount of silver halide into light-sensitive layers leads to some disadvantages such as an increase in light scattering in the emulsion layers and consequently, a decrease in sharpness of the images formed, and in addition, an increase in the processing time for the light-sensitive materials due to an increase in the thickness of the emulsion layers. Furthermore, the formation of dyes with these couplers is not completed during color development and thus it is necessary to use strong oxidizing agents in subsequent processing steps to complete the dye formation.
In order to improve these defects, two-equivalent yellow color forming couplers have been employed, which require only two moles of exposed silver halide to form one mole of azomethine dye.
The two-equivalent yellow color forming couplers, in general, have chemical structures in which one of the hydrogen atoms of the active methylene group is substituted with a releasable atom or group. Examples of such releasable atoms or groups are a fluorine atom as described in U.S. Pat. No. 3,277,155, a phenoxy group as described in U.S. Pat. No. 3,408,194, an acyloxy group as described in U.S. Pat. No. 3,447,928, a sulfoxy group as described in U.S. Pat. No. 3,415,652, and a group having a saccharin structure as described in U.S. Pat. No. 3,730,722.
However, these couplers are not sufficient for use in color photography because they are accompanied by disadvantages in that the coupling reactivity is insufficient, in that a marked color fog is produced, in that the couplers per se are unstable and their coupling activities decrease or color stain occurs in the light-sensitive materials during storage, in that the yellow color images formed are unstable or in that the preparation of the couplers is quite difficult.
As couplers which improve these defects, there are the yellow color forming couplers having a releasable group derived from imide compounds described, for example, in Japanese Patent Application OPI Nos. 26,133/1972, 29,432/1973 and 73,147/1973.
However, use of these couplers is still accompanied by either of the following undesirable properties. That is, developed silver which is formed during the color development step of color processing is not removed completely in subsequent processing steps using a bleaching bath and a fixing bath or in a subsequent processing step using a blixing bath containing a silver complex forming agent and an oxidizing agent and remains in the final photographs to adversely affect the color reproduction. The coupler does not provide a sufficiently high color density without using a color developer solution containing benzyl alcohol which tends to increase the biological oxygen demand (BOD) and it is undesirable to use benzyl alcohol in view of environmental pollution, particularly, water pollution. The sufficient color density which is required for providing good color reproduction can not be obtained where a relatively small amount of a high boiling solvent for the coupler, which is used to dissolve the coupler and is incorporated into a photographic material together with the coupler, is employed. The photographic properties of a color image obtained are markedly influenced by variations in the pH of the color developer solution used.